The invention relates generally to a processing of information from an optical disk layer, and more particularly to a method and system for processing information from optical layers of a holographic data storage medium.
Generally, holographic storage is the storage of data in the form of holograms, which are images of three dimensional interference patterns created by the intersection of two beams of light in a photosensitive storage medium. Both page-based holographic techniques and bit-wise holographic techniques have been pursued. In page-based holographic data storage, a signal beam, which contains digitally encoded data, is superposed on a reference beam within the volume of the storage medium. This results in a chemical reaction thereby, changing or modulating the refractive index of the medium within the volume. This modulation serves to record both the intensity and phase information from the signal. Each bit is therefore generally stored as a part of the interference pattern. The hologram can later be retrieved by exposing the storage medium to the reference beam alone, which interacts with the stored holographic data to generate a reconstructed signal beam proportional to the initial signal beam used to store the holographic image.
In bit-wise holography or micro-holographic data storage, every bit is written as a micro-hologram, or Bragg reflection grating, typically generated by two counter-propagating focused recording beams. The data is then retrieved by using a read beam to reflect off the micro-hologram to reconstruct the recording beam. Accordingly, micro-holographic data storage is more similar to current technologies than page-wise holographic storage. However, in contrast to the two layers of data storage that may be used in DVD and Blu-ray Disk formats, holographic disks may have multiple layers of data storage, providing data storage capacities that may be measured in terabytes (TB). Thus, the holographic storage medium stores information throughout the volume of the storage medium in multiple layers from about 50 to 100 layers. In order to read or record data in such multiple layers, the holographic storage medium must be complemented with a system and a method for focusing the objective lens of a pick-up head to an optimal depth of the layer on which the symbols of the selected layer are recorded.
Therefore, there is a need for a method and system for efficient processing of information from a multilayer holographic data storage medium.